Interpretive Summary: The recent expansion of the ethanol industry has increased the availability of ethanol by-products as a likely feed source. These by-products can be efficiently used by ruminants and are readily available in the Southern Great Plans. However, the most effective source and concentration in feedlot diets is not known. Additionally, the sulfur content of distillers grain can be high and increase the likelihood of sulfur being reduced in the rumen to hydrogen sulfide. The ruminal production of hydrogen sulfide can cause polioencephalomalacia, which is potentially fatal and reduces performance in feedlot cattle. Therefore, a study was conducted to evaluate the effects of wet distiller's grains with solubles (WDG) on in vitro dry matter disappearance, in vitro rate of gas production, hydrogen sulfide production, and volatile fatty acid production. Treatments included concentration of WDG (15 or 30%) and source of wet distiller's grain (corn or sorghum) plus a 0% WDG control. Steam-flaked corn was the base-ingredient used in all treatments. The control treatment had greater in vitro dry matter disappearance and rate of gas production than treatments containing WDG. Treatments containing corn-based WDG had greater rate of gas production and in vitro dry matter disappearance than treatments containing sorghum WDG. Hydrogen sulfide production was increased as the inclusion of WDG increased. There was little effect among treatments in the proportions of major volatile fatty acid production and concentration.
Our results suggest that including either source of WDG in the diet decreased in vitro dry matter disappearance and gas production. Furthermore, corn WDG seemed to be more digestible than sorghum WDG. Hydrogen sulfide production increased with increasing level of WDG in the diet, which potentially reflects a greater sulfur concentration in WDG

Technical Abstract:
The effects of wet distiller's grains with solubles (WDG) on in vitro rate of gas production, in vitro dry matter disappearance (IVDMD), hydrogen sulfide (H2S) production, and volatile fatty acids (VFA) were evaluated. Five substrate treatments that were balanced for ether extract content were arranged in a 2 x 2 + 1 factorial. Factors were concentration (15 or 30%; DM basis) and source of WDG (corn or sorghum wet distiller's grains with solubles; CDG and SDG, respectively) plus a 0% WDG control in substrates with steam-flaked corn (SFC) as the basal grain. Control substrates had greater IVDMD, rate of gas production, and area under the gas production curve (AUC; P < 0.01) than WDG-based substrates. Substrates containing CDG had a greater (P < 0.05) rate of gas production, IVDMD, and area under the curve (AUC) than SDG treatments. Increased (P = 0.01) H2S production (micro-moles/g of fermentable DM) was noted as inclusion of WDG increased from 15 to 30% of the substrate. Conversely, a decrease (P < 0.05) was observed for AUC and IVDMD as the level of WDG inclusion increased. There were no differences (P > 0.10) among treatments in proportions of major VFA, acetate:propionate ratio, and total VFA concentration.
Our results suggest that including WDG in the dietary substrate decreased IVDMD and gas production measured as AUC, which was particularly evident as WDG increased from 15 to 30% of the substrate DM. In addition, CDG seemed to be more digestible than SDG. Hydrogen sulfide production increased with increasing WDG in the substrate, reflecting greater S concentration in WDG, but in vitro VFA profiles were not affected by WDG.